Desulfurizing petroleum with alkali and di-alkyl sulfoxide



United States Patent 3,184,405 DESULFURIZING PETROLEUM WITH ALKALI AND DI-ALKYL SULFOXIDE Charles 0. Hoover, P.0. Box 4294, Corpus Christi, Tex. No Drawing. Filed Mar. 13, 1964, Ser. No. 351,832 Claims. (Cl. 208-227) This invention relates to a process for desulfurizing petroleum and more particularly to a process for removing mercaptans from petroleums.

Present processes for removal of sulfur in the form of mercaptans from petroleum, particularly where the substantially complete removal of mercaptans is sought, involve relatively complicated and uneconomic operations which are generally impractical for ordinary refinery operation. Some of the very low molecular weight mercaptans are removable by washing with caustic alkali, but removal of higher molecular weight mercaptans requires elevated temperatures and more complex chemical treatments, including processes such as hydrogenation, treatment with strong sulfuric acid, and the like.

Lighter petroleum distillates, such as motor fuels and light burning oils, will more commonly be treated by socalled sweetening processes which serve merely to oxidize the mercaptans to disulfides and other forms of sulfurcontaining compounds which remain dissolved in the oil and thus do not effect any appreciable desulfurization thereof.

It is highly desirable in many instances, especially in the case of distillate fuels for use in internal combustion engines, to reduce the sulfur content in order to reduce the corrosive action of the sulfur compounds on the metal surfaces of the engines and to improve both the clear octane value of the fuels and their response to additions of tetraethyllead for anti-knock purposes. In the case of kerosene and light fuel oils, the presence of mercaptans produces bad odor, inferior burning qualities and instability in storage.

The present invention, therefore, has for its primary object, the provision of a chemical treating process which will effectively and easily remove substantially all of the mercaptan-type sulfur compounds from petroleum stocks and particularly from the lighter distillates obtained by the conventional processes for refining crude oils.

Generally stated, the process in accordance with this invention comprises admixing with a petroleum stock in the liquid phase, first, an alkali hydroxide, and second, a sulfoxide compound having the general formula:

H R-SRt wherein R and R either or both, is a methyl-, ethyl-, or propyh, group. The preferred sulfoxide is dimethyl sulfoxide (herein designated DMSO) because of its ready availability and its high efficiency in the process.

I have discovered that the critical feature of the process is that the alkali hydroxide must be first added to the oil, and thereafter, without removal or separation of the initially resulting reaction products, admixing the sulfoxide with the oil-alkali mixture. By this procedure, it is found that it is possible to effect substantially complete removal of all mercaptans initially present in the oil. The resulting oils will not only be desulfurized to the extent of the removal of mercaptan sulfur but as a result of the mercaptan removal, will also be rendered sweet to the conventional doctor test. Also, other acidic compounds originally present will be removed or greatly reduced in quantity.

My invention is based upon the discovery that sulfoxides of the character defined have exceptionally high solvent capacity for the alkali salts of the mercaptans,

"ice

namely, the mercaptides. Hence, by first reacting the mercaptans with the alkali hydroxide, and thereafter, before removal of alkali reaction products, admixing with the oil-alkali mixture at suitable proportion of the sulfoxide, substantially complete removal of the mercaptan sulfur compounds can be readily effected. Moreover, the treatment may be conducted entirely under ambient atmospheric conditions of temperature and pressure, thereby minimizing the complexity and expense of the required apparatus.

In accordance with this invention, the quantity of alkali hydroxide employed is stoichiometrically related to the quantity of sulfur present as mercaptan sulfur. Generally the alkali hydroxide will be added in the proportion of at least one mol of the alkali per mol of mercaptan sulfur present in the oil. Usually an excess of alkali will be employed to assure effective mixing and completeness of the reaction both with the mercaptans and with other acidic constituents which may be present. As the molal quantities required are quite small, even for very sour oils, a substantial molal excess of the alkali will represent only a very small quantity on a volumetric or weight basis relative to the oil being treated.

The preferred alkali hydroxide is sodium hydroxide but potassium hydroxide may also be used, although it is more expensive and less easily handled. The alkali hydroxide may be used in solid form, in which case, the powdered or granulated form is preferred. It may also be employed in aqueous solution in any concentration ranging from about 5% by weight of the solution to the maximum concentration at which it may be maintained in liquid form. Where aqueous solutions are employed, concentrations from about 30% to 50% are found most use ful with a 50% concentration preferred in most instances in order to minimize the quantity of sulfoxide required, as the solvent efiiciency of the latter for the alkali mercaptides decreases generally in proportion to the amount of water present.

Following are several examples illustrative of the present invention:

Example 1 A super sour naphtha having an initial mercaptan sulfur content of 0.91% by weight was treated with various concentrations of NaOH and differing proportions of dimethyl sulfoxide (DMSO) in accordance with the following table. In each test the oil was thoroughly agitated with the alkali for a period of 10 minutes. The oil-alkali admixture was then agitated for another 10 minutes with the listed volumes of DMSO. After settling and separating the treated oil from the DMSO solution, the mercaptan remaining in the treated oil was determined.

Reagents Final Percent Concentration percent by wt. NaOH, DMSO, R-SH Reduction mols percent by content in RSH vol. of oil Example 2 The same naphtha was treated with 1.1 mols of 50% KOH solution followed by 15% by volume of DMSO. The mercaptan sulfur was reduced to 0.003%, a reduction of 99.7%.

Example 3 A kerosene initially containing 0.012% sulfur as mercaptans was treated successively with 10 mols 50% NaOH 3 7 solution and 20% by volume of DMSO. The mercaptan sulfur was reduced to 0.00'06% by weight, a reduction of 95%. v i

' Example 4 Another kerosene having an initial mercaptan content of 0.027% by weight was treated with 2.0 mols'of 50% 'NaOH solution followed by 3.2% by volume'of'DMSO.

The final 'mercap'tan sulfur content was 0.0009% by weight, a reduction of 96.7%. a r

Example 5 of 50% NaQH followed by 20% by volume of DMSO.

duct-ion of 99.13%. v

r Example 7- :Thefinal mercaptan sulfur content was 0.0002%, a re- 7 Asour haphtha 'havingan initial 'mercapta'n sulfur content or" 0.81% by weightwas treated with 1.1 mols of 98% (solid) 'Na'OH followed by 10% by volume of.

DMSO. The mercaptan sulfur content was reduced to 0.0007%,a reductio"nof 99.1%., a

' 7 Example 8 v Asample'of the 'supe'rsour naphtha initially containing 0.91 "by'weiglitof sulfur as 'mercaptan was treated with 1.1 mol'sjof 9 8% '(solidylqaOH followed by 1"5%[-by' volume ofdithyl 'sul foxide. Thetreated oil contained 0005870 by Weight'of mercaptan sulfur, a reduction of V Example 9 65% by volumeof dipropyl sulfoxide was substituted for the diethyl sulfoxide of Example 8. 90%-of-the-mercaptan sul-fur was r'e'movedQ As 'dipropyl sulfoxide is slightly soluble in aliphatic hydrocarbons, zitwvas'dilute'd with 5% of water to "render it immiscible with the oil layer.

' The DMSO mayf'be reclaimed fofr -re-use, iif'desired, bya number of relatively simple procedures. The soluwhereiri R and R either from the resultingzadmixture.

sulfoxideis dimethyl sulfoxide.

DMSO preparatory to its re-use. The bottom product was dissolved in water and acidified, liberating an oil layer containing a high concentration of mercaptans.

.It Will be evident from the foregoing that the process in accordance with this invention not only provides an exceptionally -efiicient desulfurizing process butproduces a reaction productifrorn whichfmercaptans may be readily recovered as a valuable by-product.

It will be understood that' various modifications :and alterations maybe made in the procedures described within the scope of the appended claims but without departign from the spirit of thisinvention.

What 'I claim and desire to secure by Letters Patent is:

1. A process. for desulifur-izin'gfa mercaptan con'taining petroleum oil stock, comprising, successively admixing with said stockin the liquid phase in the following order (a) a strongalkali and ('b) a di-alkyl sulfoxide having the general-forrnu'la I v R's-R1 f or both, is methyl-, ethyl-, or .propyl-group, the'additionof the di-alkyl 'sulfoxide being made Without separation of 'reactionproducts' :from the oil stock-alkali admiXtureQand separating the treated oil '2.".A ;process according toiclaim 1 wherein the die'alkyl '3. A processaccordingato claim *1 alkaliis'sodiumhydroxide. 7 v p '4; A process, according to claim 1 wherein thestrong whereinthe strong alkali is admixed in the proportion of at least one 'mol per mol 'of mercaptan.sulfur'inxthebilstock. 5. A pro'cess in accordance'with .=clai1n 1 wherein the -strong2alkali-is an aqueous solution containing from. about '30.% to about 50%:by weight of'sodium hydroxide.

"6. Agprocess according-to claim 1-;wherein said strong alkali is solid sodium "hydroxide in particulate form. n

I 7. Azprocessaccordingto'claim: 1 'wherein said di-alkyl sulfoxideis diethyl-sulfoxide. v

I8. A iprocess for desulfurizin'g a *m'ercaptan-containing petroleum oil stoCkQcomprising, successivelyadmixing tion s'epafatin'g-frornthe oil layer-after'treatmentinaccordance with any of the foregoing examples, will "comprise a DMsO-wat'er sodium (potassium) trierca'ptide hy- -dro'carbon solution. Ino'ne-procedure the separated'solution may b'e'neutrali'zed Withasuitable acid. This springs I mercaptan's and dissolved hydrocarbons which will sepa- 1 rate 'as a layer on top of the aqueous DM SO-salt solution; The latter will'be separated from the upper layer material and vacuum distilled, evaporating the 'DMSO-water solution overhead and separating itfrom nonvolatile matter. The DMSO Wa'ter overhead productcan then be .further jfr ac'tiona'ted under vacuum to recover practically pur'e 'DMSO. I p v r Another-procedureis -to subject-the bottomJayer solu-' V tion directly to vacuum distillation. ,The'DMSO-water was distilled overhead, leaving a bottom product containing the sodium mercaptides." The overhead material-may be further purified -to reducethe water content of the with 'said 's'tock'in'the liquid vphase in the following-order: (-c'l.) "sodium hydroxide in the proportion of. at least =one -mol per mol'ofimercaptan sulfur in said stock to form the corresponding-sodium mercaptides,-and (b) dimethyl sulfoxide inangamount 'suflicientto dissolve said'sodiurn mercaptides, :the addition of the dimethyl sulfoxide' being made withoutaseparation ofreaction products from oil stock-sodium hydroxide admixture -'and separating the -treated oil -from the dimethyl sulfoxide solution.

9 A -process*according tovclaim '8 whereinsaid-sodium hydroxide 'is employed in .a state varying from'aqueous solutions ornom about 5% to about concentrations to solid particulate forms. j

1-0.. A process according to claim 9 wherein said amount -of dimethyl sulfoxide is in the range from about 3.0%

ALPHONSO D. SULLIVAN. Primary Examiner.

to about 50% byvolu'me of saidoil stock.

' ReferencesCited by theExaminer UNITED STATES'PATENTS "2,365,898 12/44 Morrisret al. 208240 2927,0761 3/60 Jolly 208237 3,052,626 9762 Ferrara :20s -'231 

1. A PROCESS FOR DESULFURIZING A MERCAPTAN-CONTAINING PERTROLEUM OIL STOCK, COMPRISING, SUCCESSIVELY ADMIXING WITH SAID STOCK IN THE LIQUID PHASE IN THE FOLLOWING ORDER (A) A STRONG ALKALI AND (B) A DI-ALKYL SULFOXIDE HAVING THE GENERAL FORMULA 